Muscle Relaxant: what is it?
Drugs that reduce the tension in skeletal muscles. They are used to treat muscle spasms (involuntary and often painful contractions of muscles caused by injury or disease) and spasticity, in which the muscles are continually in a state of increased tension or rigidity due to such disorders as multiple sclerosis and cerebral palsy.
Muscle relaxants either act centrally (i.e. on the brain or spinal cord), to inhibit the nerve signals that cause the muscles to contract, or directly on the muscles themselves, to prevent the activity in the cells that cause the muscles to contract.
The dosage of these drugs may need some adjustment to obtain the optimum that controls symptoms but does not cause muscle weakness. Skeletal muscle relaxants should not be stopped abruptly or stiffness may be worse than before treatment.
The muscle relaxants used in surgery during general anaesthesia work in a different way. They act at neuromuscular junctions (where the nerve fibre meets the muscle it supplies)
to block the transmission of nerve impulses, either by binding to receptor sites normally occupied by the chemical transmitter acetylcholine (nondepolarizing muscle relaxants, such as pancuronium and mivacurium )
or by mimicking the action of acetylcholine, making the muscle no longer receptive to stimulation by this transmitter (depolarizing muscle relaxants, such as suxamethonium).
Drugs that relax smooth muscle include antispasmodics, bronchodilators, and vasodilators.
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